Budget stay in St.Petersburg, Russia

Hi! I need a piece of advice - my friends from Germany are planning to come to St.Petersburg in the middle of May. They are students and got used to budget hotels and couchserfing, but this time I can't share my flat with them. I need some hotel or hostel - cheap, cool and central. People say cuba hostel is fine or atmo hostel - but I don't like the photos. Seem to be too basic. I've found friends hostel - look great, but found only few reviews from foreigners. If we book Friends hostel on Griboedova, which I like most, what would one recommend on a budget around this location? I need some opinion and advice please!